Histology and ultrastructure of the neurohypophysis of the south american lungfish,Lepidosiren paradoxa

Summary The neurohypophysis of the South American lungfish Lepidosiren paradoxa has been studied with light and electron microscopy, including the Falck-Hillarp technique for catecholamines. The pars nervosa hypophyseos is a well-marked, dorsally located subdivision of the pituitary gland composed of lobes or follicles, each one constituted of a central core of ependymal cells, a subependymal hilar region made up of nerve fibers and a peripheric palisade zone of nerve endings which contact capillary vessels. Four types of neurosecretory axons can be distinguished under the electron microscope. Type I, the most common, contains spherical elementary granules of high electron density, 1500–1800 Å in diameter. The scarce type II axons contain irregularly-shaped elementary granules. Type III contains only small clear vesicles, 400–600 Å in diameter. Type IV, mostly present in regions of the gland contacting the pars intermedia, contain large granulated vesicles, 900–1000 Å in diameter. The Falck-Hillarp technique revealed axons with a positive reaction for catecholamines at sites corresponding approximately to the location of type IV of the electron microscope.Ependymal cells are of large size, linking the cerebrospinal fluid, the nerve endings and the blood vessels. A conspicuous membrane-bound, spherical dense material, 1400–2000 Å in diameter, is observed in both the apical and vascular processes of these cells. The ependymal processes which traverse the hilar and palisade regions contain structures resembling degenerated neurosecretory axons. These results are discussed in relation with the currently available information on the comparative anatomy of the pars nervosa. The possible functional significance of ependymal cells and of each type of axon are also discussed.This study was aided by the following grants: NIH NS 06953 to Prof. De Robertis, Consejo Nacional de Investigaciones Científicas y Técnicas to Prof. Zambrano, Comisión de Investigaciones Científicas de la Provincia de Buenos Aires and Comisión de Investigaciones Cientificas de la Universidad Nacional de la Plata: to Prof. Iturriza.The authors are indebted to Prof. De Robertis for his generosity in granting us his laboratory facilities, and to Dr. F. J. J. Risso and Mr. A. Fernández (Resistencia, Chaco) who provided the specimens used in this study. The able microtechnical assistance of Miss L. Riboldazzi and Mrs. R. Raña and the photographic work of Mr. A. Saenz are much appreciated.Members of the Scientific Career, Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina.     

The hypothalamo-hypophysial system of the frog Rana temporaria

Summary The median eminence (ME) of the adult frog, Rana temporaria, was studied by means of electron microscopy including quantitative electron-microscopic autoradiography. In frogs captured in May and June numerous peptidergic neurosecretory fibres extending via the internal zone to the pars nervosa display large swellings containing few granules, mitochondria, neurotubules and cisternae of the smooth endoplasmic reticulum. In addition, few secretory globules up to 1.5 m in diameter occur in these varicosities. In animals collected during the autumn period many of these neurosecretory swellings filled with neurosecretory granules and polymorphic inclusions resemble Herring bodies. Three types of granule-containing neurosecretory fibres were observed in the external zone (EZ) of the ME of adult R. temporaria. Peptidergic A₁- and A₂-type fibres are characterized by granules 150–220 nm and 100–160 nm in diameter, respectively. Monoaminergic fibres of type B with granules approximately 100 nm in diameter represent 50% of all neurosecretory elements in the EZ of the frog ME; 12% of the total number of granule-bearing axons in the EZ actively taking up radiolabelled 5-hydroxytryptophan are thought to be serotoninergic terminals. Neurosecretory terminals of all types and glial vascular endfeet establish direct contacts with the perivascular space of the primary portal capillaries. Some neurosecretory terminals are separated from the lumen of the third ventricle by a thin cytoplasmic lamella of tanycytes. The possible physiological significance of this structural pattern is discussed.     

Morphometric classification of the neurosecretory granules in the rat pars nervosa

Summary The distribution of the diameters of the neurosecretory granules in the rat pars nervosa (measured from electron micrographs taken at 40 000 × ) was compared among axons by nonparametric statistical methods and the axons were classified into five groups with median granule diameters of 143, 155, 167, 180 and 193 nm. We suggested that these five axon types carried different secretory substances contained in the pars nervosa. This investigation is supported by a grant from the Population Council, New York and grant from the Ministry of Education. Authors are grateful to Japan Electron Optics Laboratory Company for their technical assistance with the electron microscopy and to Miss Kazue Yamamoto for her help in preparing the figures.     

The neurohypophysis of the crested newt

Summary In the crested newt, the ultrastructural organization of the pars nervosa is analogous to that already known in non-mammal tetrapods. An orderly array of ependymal cells makes up the inner limiting layer while less abundant pituicytes are irregularly distributed within this organ. Light and dark pituicytes can be distinguished on the basis of the relative density of the cytoplasmic matrix and the distribution of the cell organelles.Both the ependymal cells and pituicytes are rich in dense bodies and possess extensive processes which ramify among the nerve fibers, often reaching the pericapillary space which they can line for long distances.The main components of the pars nervosa are nerve fibers and nerve terminals (type A), containing electron dense granules 1200–2000 Å in diameter together with clear vesicles averaging 250–400 Å. These fibers are likely to correspond to the aldehyde fuchsin positive neurosecretory fibers revealed by light microscopy. Differences in the granule size within the fibers and terminals lead to further recognition of two subgroups (A₁ and A₂).Other fibers and terminals (type B) containing clear vesicles and granular vesicles 600 to 1000 Å in diameter, possibly of aminergic type, are also encountered. These fibers are rare and can be seen only in the portion of the pars nervosa near the pars intermedia of the adenohypophysis.Lastly, fibers and terminals containing only clear vesicles ranging from 250 to 400 Å (type C) are occasionally found.Nerve endings are often formed by type A fibers on the perivascular space and on the perivascular processes of the ependymal cells and pituicytes. In agreement with recent findings available in the literature, the occurrence of synaptoid contacts between these terminals and both pituicytes and ependymal cells may confirm the active role of these cells in transport and release of neurosecretion.Work supported by a grant from the Consiglio Nazionale delle Ricerche.We are gratefully indebted to Dr. G. Gendusa and P. Balbi for technical assistance, dr. G. E. Andreoletti for statistical analysis.     

Seasonal plasticity of the pituitary pars intermedia of the one-humped camel (Camelus dromedarius)

The pituitary pars intermedia of Camelus dromedarius is well developed and completely surrounds the pars nervosa. Two major groups of cells are present: endocrine (ec) and glial-like cells (glc). The ec group is composed of three morphologically distinct cell types. Type I, or polyhedral light cells (LC-I) and type II, or polyhedral dark cells (DC-II), have secretory granules of heterogeneous electron density whose size ranges from 170 to 300 nm. Type III cells are elongated with homogeneous electron-dense secretory granules of 80–200 nm. The glc make up an organized network, form follicles in the centrolobular zones and are positive for vimentin and S-100β immunolabelling. The nerve fibres penetrating the lobe are numerous, and can be classified into two types according to the membrane bound vesicles found in their endings (ne). Ultrastructural quantitative analysis revealed significant variations in PI elements between winter and summer seasons (F = 8.014, p = 0.006). DC-II cells characterized by developed biosynthetic machinery and a large pool of secretory granules storage are increased with the ne in winter. However, LC-I cells showing frequent cytoplasmic degranulation are predominant with glc in summer. Thus, important cellular remodelling occurs in the dromedary PI that may depend upon, or perhaps anticipate, external living conditions.     

The Pituitary Gland of the Roach Leuciscus rutilus

Three different endocrine cell types were identified by electron microscopy in the rostral pars distalis (RPD) of the roach, Leuciscus rutilus. The cells which are characterized by the morphology and sizes of their secretory granules are assumed to secrete prolactin, ACTH and TSH. Prolactin cells occur in two forms which could be separated on account of the sizes of their granules. Intra-peritoneal injections of reserpine had a strong and persistent effect 24 hours after the treatment. The prolactin cells with small granules reacted with a marked release of secretion. The border of the RPD is composed of a so-called double basement membrane in contact with the perivascular spaces and forms extensive ramifications into the rostral neurohypophysis (RNH). Nerve fibers of different categories terminate at the border and its network in the RNH. Substances released from these terminals may influence the endocrine cells of the RPD. The ACTH cells and the prolactin cells are innervated by axons with granules less than 100 nm. The nomenclature of type ‘A’ fibers and ‘B’ fibers is discussed because it was difficult to make a reliable discrimination of the fibers and their nature by the sizes of their granules. However, four types of nerve fibers were distinguished in connection with the RPD although the presence of more types was indicated. In all four types the size variations of the granules are great and overlapping. The average sizes of the granules in these fibers are 157, 114, 119 and 81 nm. The origin of the nerve fibers innervating the RPD is discussed. All morphological data indicate a complex hypothalamic control of the RPD of the roach.     

Fine structure of the median eminence and the pars nervosa of the bullfrog,Rana catesbeiana

Summary The hypothalamic neurosecretory system of the bullfrog, Rana catesbeiana, was studied with light- and electron microscopy. The median eminence is roughly divided into two portions. The upper portion mostly consists of ependymal cells, glial cells and preoptico-hypophysial nerve tract, whereas in the lower portion, neurosecretory axons, glial cells, processes of glial and ependymal cells, and fine blood vessels of the hypothalamic portal vein are located. A part of the neurosecretory axons of the preoptico-hypophysial tract proceeds to the lower portion of the median eminence. These axons are arranged perpendicularly to the capillaries of the hypothalamic portal vein. The glial cells are densely located in the area of the median eminence where neurosecretory material is abundant. The neurosecretory material in the neurosecretory cells, their axons, the median eminence and the pars nervosa of the bullfrog shows a positive reaction to PAS treatment.The neurohemal area of the median eminence is occupied by many neurosecretory and non-neurosecretory axons, containing neurosecretory granules and/or synaptic vesicles. The axonal portions with the synaptic vesicles which are considered to be the nerve endings abut on the capillaries of the portal system. The size of synaptic vesicles in the axon terminals containing few neurosecretory granules is larger than those in the endings with many neurosecretory granules. Infrequently glial and ependymal processes are interposed between the nerve endings and the capillary wall.In the hilar region of the infundibulum, synapses are frequently observed between the thin fibers with or without neurosecretory granules and dendrites of non-neurosecretory neurons. The probable functions of these synapses are briefly discussed on the basis of our findings. Both in the hilar region of the infundibulum and in the pars nervosa, electron-dense neurosecretory granules of two different sizes were observed. The median eminence contains only one type of granules.The fine structure of the pars nervosa shows similar structures to those of the median eminence. Both in the median eminence and the pars nervosa, the fenestrated endothelium of the capillaries was frequently observed. The thick perivascular connective tissue space containing fibroblasts and collagen fibrils was observed both in the median eminence and the pars nervosa. Vesicles in the cytoplasm of the endothelial cells which appear to take a part in the transendothelial transport were observed.This investigation was supported in part by United States Public Health Service Research Grant, No. A-3678, to Hideshi Kobayashi from the National Institute of Arthritis and Metabolic Diseases and partly by a grant for Fundamental Scientific Research from the Ministry of Education of Japan. The authors wish to express their thanks to Prof. K. Takewaki for his kind encouragement.     

The hypothalamo-hypophysial system of hypophysectomized rats

Summary The median eminence (ME) of hypophysectomized rats was studied by means of light and electron microscopy. Paraldehyde-fuchsin (PAF)-positive material is seen in the external zone (EZ) of the ME 2–5 days after the operation. Its amount gradually increases especially in the caudal part of the ME during the following few days. Some PAF-positive fibers make contact with the subependymally located blood capillaries. In the most caudal region of the recessus infundibuli they penetrate into the third ventricle. PAF-positive material decreases markedly from the ME of rats two months after hypophysectomy and exposure to a 1% salt load. Fibers of types A₁, A₂ and B containing granules of 120–220 nm, 100–150 nm and 80–100 nm in diameter, respectively, are seen in the EZ of the ME in hypophysectomized rats, although almost exclusively A₂- and B-type structures make contact with the primary portal capillaries in intact animals. All types of neurosecretory fibers establish contact with the subependymal nonfenestrated blood capillaries and penetrate the recessus infundibuli. Some neurosecretory terminals of different types make direct contact with the glandular cells of the pars tuberalis or are separated from them by a thin basal lamina. It is assumed that mainly neurosecretory fibers of types A₂ and B are permanently connected with the primary portal capillaries in the EZ of the ME in intact mammals, while the overwhelming majority of fibers of A₁-type shows ingrowth during the course of postoperative reparation. The possible physiological significance of the described changes is discussed.     

The pars intermedia of the mink,Mustela vison

Summary The pars intermedia of intact and experimental female minks has been studied by light, electron and fluorescence microscopy. The general structure of the mink intermediate lobe is described. Two main cell types are recognized. One, termed glandular cell, predominates in number and is characterized by the presence of electron-dense granules about 200 nm in diameter and numerous large vesicles up to 300 nm in diameter. The other, termed stellate cell, is devoid of cytoplasmic vesicles and granules and possesses microfilaments, junctional complexes and elongated processes inserted between the glandular cells. Different treatments (photostimulation and administration of hypertonic saline and metopirone) induced morphological reactions in the glandular cells. The significance of these changes and the possibility of a functional relation between the pars intermedia and ACTH secretion are discussed.Numerous nerve fibres and axon terminals containing electron-dense granules (60–120 nm) and electron-lucent vesicles (30–40 nm) are observed throughout the pars intermedia.With the histochemical fluorescence method of Falck-Hillarp a rich system of delicate fluorescent varicose fibres, sometimes provided with irregular swellings or droplets, is observed in the pars intermedia and also in the pars nervosa. Microspectrofluorometrically these fibres exhibit the spectral characteristics of catecholamines. All the cells of the pars intermedia and a large number of cells in the pars distalis show a yellowish weak fluorescence, which becomes much stronger after combined formaldehyde-ozone treatment. This cellular fluorophore shows the same microspectrofluorometric characteristics as does the fluorophores of tryptamine and of certain peptides with NH₂-terminal tryptophan.Supported by the Swedish Fur Breeders' Association and the Swedish Natural Science Research Council (grant No. 2124). Thanks are due to Miss W. Carlsson and Miss Y. Lilliemarck for their helpful technical assistance.Supported by the Harald and Greta Jeanssons Stiftelse and by the Ford Foundation. The skilful technical assistance of Mrs. Eva Svensson and Miss Annika Borgelin is greatfully acknowledged.     

Morphology of identified neurosecretory and non-neurosecretory cells in the cockroach pars intercerebralis

Electrophysiologically identified cells of the cockroach pars intercerebralis (Periplaneta americana) were injected with the dye Lucifer Yellow for morphological examination and with horseradish peroxidase for ultrastructural marking. In addition to this, uninjected cells were also studied to elaborate the findings from the injected material. The two electrophysiologically distinct classes of cells (type I and type II) correspond to two distinct morphological and ultrastructural classes. Type I cells are the medial neurosecretory cells of the pars intercerebralis, which project their axons to the retrocerebral neuro-hemal complex. Their cell bodies have a mean diameter of 17 microns, and they contain neurosecretory granules 200 nm in diameter. Arborizations emanate from the axon in the anterior part of the protocerebral neuropil. The type II cell bodies are larger (38 microns in diameter). Their axons project into the contralateral circumesophageal connective. These cells were usually multipolar, having somatic arborizations in the anterior portocerebral neuropil. The cell bodies contain vesicles 40 nm in diameter, numerous trophospongia, and a multi-layered glial envelope.     

The neurohypophysis of the crested newt

Summary In the median eminence of the newt a medial region and two lateral regions are described.In cross section, the medial region appears to be made up of 1) an outer or glandular zone (Zone I) containing aldehyde-thionine-positive and negative nerve fibres and blood capillaries. Nerve fibres appear aligned in palisade array along the capillaries. 2) An inner zone (Zone II) made up of a) a layer of aldehyde-thionine-positive nerve fibres (fibrous layer) belonging to the preoptic hypophyseal tract and b) a layer of ependymal cells lining the infundibular lumen and reaching the blood vessels with their long processes.The lateral regions display a less pronounced stratification and aldehyde-thionine positive nerve fibres are nearly absent.A slender lamina (ependymal border) containing mainly aldehyde-thionine-positive nerve fibres and ependymal cells connects the median eminence to the pars nervosa.At the ultrastructural level, in the outer zone of the medial region at least 4 types of nerve fibres and nerve endings are identified:Type I nerve fibres containing granular vesicles of 700–1000 Å and clear vesicles (250–400 Å).Type II nerve fibres containing granular vesicles and polymorphous granules of 900–1300 Å and clear vesicles (250–400 Å).Type III nerve fibres containing dense granules of 1200–2000 Å and clear vesicles of 250–400 Å.Type IV nerve fibres containing only clear vesicles of 250–400 Å. In the inner zone too, all these nerve fiber types are found among ependymal cells, while the fibrous layer consists of nerve fibres containing granules of 1200–2000 Å in diameter.In the lateral regions Type I, Type II and Type IV nerve fibres and their respective perivascular terminals are found; axons containing dense granules (1200–2000 Å) are scanty. In these regions typical synapses between Type I nerve fibres and processes rich in microtubules are visible.The classification and functional significance of nerve fibres in the median eminence are still unsolved, but it may be assumed that nerve fibres of the medial region belong to both the preoptic hypophyseal and tubero hypophyseal tract, while the lateral regions are characterized by nerve fibres of the tubero hypophyseal tract. Peculiar specializations of the ependymal cells in the median eminence of the newt are also discussed.Work supported by a grant from the Consiglio Nazionale delle Ricerche.The authors are indebted to Mr. G. Gendusa and P. Balbi for technical assistance.     

Two types of neuromuscular junctions in the pharyngeal retractor muscle ofHelix lucorum

The pharyngeal retractor muscle of the snailHelix lucorum is innervated by a pair of nerves containing axons of two types, for which there are two corresponding types of myoneural junctions with the muscle cells. The junctions of type I correspond to the thick axons. The terminals of these axons, which contain numerous spherical transparent vesicles (41±5 nm) and fewer vesicles of the dense-core type (67±3 nm), make contact mainly with noncontracting sarcoplasmic projections of the muscle cells. Junctions of type II correspond to thin axons, containing many granules. The terminals of these axons make contact with contractile parts of the muscle cells and they contain a heterogeneous population of vesicles: small spherical clear vesicles (44±2 nm), granules with fine-grained contents (135±5 nm), and a few spherical dense-core vesicles. The distance between the muscle cells is usually great — over 50 nm, but in the region of the sarcoplasmic processes the surface membranes come together to form a gap which in some areas does not exceed 10 nm.N. K. Kol'tsov Institute of Developmental Biology, Academy of Sciences of the USSR, Kiev. Translated from Neirofiziologiya, Vol. 9, No. 5, pp. 539–542, September–October, 1977.     

Rostrocaudal variation of fiber type composition in rat intercostal muscles

Summary We used the histochemical stain for ATPase to compare the fiber-type composition of rat internal and external intercostal muscles from thoracic (T) segments 2–5, 8, and 11. At each level, type II fibers were more numerous than type I fibers, type II B fibers were more numerous than II A fibers, and type I fibers were more numerous in external than in internal intercostals. However, fiber type composition varied from segment to segment. For example, the proportion of type II A fibers increased in a rostrocaudal gradient in internal but not external intercostals, and type I fibers were more prevalent at rostral and caudal than at intermediate levels in both internal and external intercostals. These results provide a basis for interpreting previous physiological and molecular studies which have compared intercostal muscles from different segmental levels.     

Fine structure of the autonomic nerves of the rabbit myometrium

Summary The fine structure of the preterminal nerve fibers of the rabbit myometrial smooth muscle was studied using potassium permanganate fixation or glutaraldehyde fixation with postosmification. The preterminal fibers were mostly formed by 2–10 axons enveloped by Schwann cells. Two kinds of axons and axon terminals were found. (1) Adrenergic axons, which contained many small, granular vesicles (diameter 300–600 Å) and large granular vesicles (diameter 700–1200 Å) which represented ca. 2% of the total count of the vesicles. (2) Nonadrenergic axons, which contained small agranular vesicles (diameter 300–600 Å) and large granular vesicles (diameter 700–1200 Å). Both types of axons formed preterminal varicosities along their course. The real terminal varicosities, representing the anatomical end of the axons, were usually larger than the preterminal ones and showed close contact to the plasma membranes of the smooth muscle cells. Both adrenergic and nonadrenergic terminals were found close to the smooth muscle cells, but a gap of at least 2000 Å was always present between the two cell membranes. The axons and preterminal varicosities of both types of nerves were in intimate contact with each other within the preterminal nerve fiber. Axo-axonal interactions between the two types of axons are possible in the rabbit myometrium. The relative proportion of the nonadrenergic axons from the total was about one fourth.     

Innervation of the intestine in the bivalve mollusc Chione stutchburyi

Summary The innervation of the gut of the venerid bivalve mollusc, Chione stutchburyi, has been examined by fluorescence histochemistry, electron microscopy and autoradiography. Specific green and yellow varicose fluorescent fibres indicate the presence of dopaminergic and serotonergic axons, respectively. Three different types of axons can be distinguished by the morphological characteristics of their vesicles. Type I axons contain predominantly small granular vesicles (average diameter 65 nm), Type II axons possess large granular vesicles (average diameter 100 nm) and Type III axons contain large opaque vesicles (average diameter 150 nm). The granular vesicles in both Types I and II axons react positively to dichromate, and their granularity is reduced by reserpine indicating that they are monoaminergic. Only Type I axons accumulate tritiated dopamine and are selectively damaged by 6-hydroxydopamine. It is concluded that Type I axons are dopaminergic. Type II axons are serotonergic: they alone take up tritiated 5-hydroxytryptamine, and 5,7-dihydroxytryptamine selectively causes degenerative changes in these axons. Type III axons contain an unidentified neurotransmitter substance. The large opaque vesicles of these axons do not react to dichromate and are unaffected by reserpine, 6-hydroxydopamine or 5,7-dihydroxytryptamine.     

Laminar ultrastructure of the dorsal cochlear nucleus in rats

The laminar ultrastructure of the dorsal cochlear nucleus was studied in ultrathin wide frontal sections, passing through all layers of the nucleus, placed on blinds with a Formvar film. The ultrastructural characteristics of cells corresponding to the cell types distinguished previously by light microscopy are described. The laminar distribution of the axon terminals was studied. In the surface and middle layers of the neuropil, by contrast with the deep layer, large branching terminals measuring 6–8 µ with spherical synaptic vesicles 40–50 nm in diameter, small terminals measuring 1–3 µ with spherical synaptic vesicles 45–60 nm in diameter, and thin unmyelinated fibers running perpendicularly to the plane of the section were predominant. On transition from the middle to the deep layer there was a corresponding increase in the number of myelinated axons and large oval-shaped terminals measuring 4–6 µ, with central mitochondria and neurofilaments, and also with spherical synaptic vesicles 50–60 nm in diameter, in the neuropil. In the surface and middle layers granular cells also were more numerous than in the deep layer. The functional significance of terminals of each type is discussed.N. A. Semashko Moscow Medical Stomatologic Institute. Translated from Neirofiziologiya, Vol. 10, No. 4, pp. 368–374, July–August, 1978.     

Ultrastructure of the pars intermedia of the adult sheep hypophysis

Summary Light microscopy of coronal sections of the sheep pars intermedia revealed a compact, incompletely lobulated V-shaped region about 15–20 cells thick, situated between the pars distalis and the pars nervosa. A prominent hypophysial cleft and follicles containing a colloid-like substance were seen.Using electron microscopy, five cell types could be distinguished: pars intermedia glandular cells, pars distalis-like glandular cells, interstitial cells, follicular cells and cleft lining cells. The polyhedral to pear-shaped pars intermedia glandular cells predominated. They contained dense-cored, membrane-bound granules near the Golgi complex, and larger, irregular vesicles with finely granular contents of varying electron density throughout the remaining cytoplasm; exocytotic release of granules was occasionally observed. Smaller numbers of cells resembling those seen in the pars distalis were scattered throughout the pars intermedia. Interstitial cells usually possessed elongated cytoplasmic processes which extended between the glandular cells, and were characterized by deeply indented nuclei, elaborate junctional complexes and an absence of cytoplasmic granules. Cells lining the follicles resembled the interstitial cells. The major cells bordering the hypophysial cleft were triangular in section and bore irregular microvilli on their free surface. The pars intermedia appeared to be less vascular than the remainder of the hypophysis and only occasional fenestrated capillaries were seen. Nerve profiles were rare.     

A whole range of fine structural criteria for immunohistochemically identified LH cells in rats

Summary Pituitaries from normal, young and adult male rats were fixed either in sublimate-formalin or in glutaraldehyde-osmium. In adjacent Paraplast sections, almost all the gonadotrophs were immunostained with both LH and FSH antisera. The rat LH and FSH antisera used were shown to be highly specific by the absorption test and by double antibody radioimmunoassay. Thin and thick adjacent Epon sections were prepared for EM and immunohistochemical examination. Cells stained with the rat LH antiserum were identified by LM, and then observed in detail by EM. On the basis of these observations we suggest that the LH cells are arranged in a sequence of basophils, i.e., Types II/III, III, III/IV and IV: Type II/III basophils are elongate with a cytoplasmic process and less vesiculated. They have morphological features of Type II (classical thyrotrophs) and also of Type III basophils. Type III basophils are oval in shape and moderately vesiculated. Both Types II/III and III basophils can be divided into two classes of cell characterized mainly by the existence of only small secretory granules (150–220 nm in diameter) (Type A) or by the coexistence of small and large (350–500 nm) (Type B). Type III/IV basophils are cells intermediate between types III and IV basophils, and moderately vesiculated with an abundance of secretory granules (150–300 nm in diameter). Type IV basophils are large, spherical or oval cells whose RER cisternae are conspicuously dilated; they contain less numerous secretory granules (150–300 nm in diameter). It is concluded that LH cells are not a single cell type, but include a wide range of subtypes.     

Ultrastructure of the corpus cardiacum and corpus allatum of the house cricket Acheta domesticus

Summary The ultrastructure of the corpus cardiacum (CC) and corpus allatum (CA) of the house cricket, Acheta domesticus, is described. Axon profiles within the CC contain neurosecretory granules 160–350 nm in diameter which are indistinguishable from those found in type I neurosecretory cells of the pars intercerebralis and in the nervus corporis cardiaci I. The CC itself contains two cell types: intrinsic neurosecretory cells and glial cells. Intrinsic NSC cytoplasm contains Golgi bodies and electron dense neurosecretory granules 160–350 nm in diameter. Synaptoid configurations with 20–50 nm diameter electron lucent vesicles were observed within axon profiles of the CC. The structure of the CA is relatively uniform with one cell type predominating. Typical CA cells possess large nucleoli, active Golgi complexes, numerous mitochondria, and occassional microtubules. Groups of dark staining cells scattered throughout the CA of some animals were interpreted as evidence of cellular death.This work was done while JTB was supported by USPHS Training Grant HD-0266 from NICHDI wish to express my thanks to Dr. Richard A. Cloney for sharing his expertise in electron microscopy     

On the vegetative network of guinea pig thoracic spinal cord

Summary A dense AChE-positive network was visualized by light microscopy in the thoracic spinal cord of grown-up guinea pigs of both sexes (bodyweight 250–300 g). This network connects in a horizontal and vertical direction the preganglionic sympathetic nuclei (n. intermediolateralis pars principalis (ILp), n. intermediolateralis pars funicularis (ILf), n. intercalatus spinals (IC), n. intercalatus pars paraependymalis (ICpe), (Petras and Cummings, 1972) all along the thoracic spinal cord. In addition to AChE activity, the bundles of fibers of this network also show a strong formaldehyde-induced NA fluorescence.Electron microscopy demonstrated granular vesicles in the cytoplasm of ILp cells. The surface of the ILp and IC neurons is almost entirely covered with synaptic buttons which have clear and granulated synaptic vesicles. The bundles of fibers consists of parallel myelin-free axones and dendrites. On their cource the axones form varicosities. In the varicosities and in the synaptic enlargements there are also clear and granulated (40–100 nm) vesicles. The probable origin of the vegetative network fibers of guinea pig thoracic spinal cord is discussed.